40 • Xtium-CL PX4 Reference Xtium-CL PX4 User's Manualby the acquisition linescan camera. The Xtium-CL PX4 supports single or dual phase shaft encodersignals. Dual encoder signals are typically 90 degrees out of phase relative to each other andprovide greater web motion resolution.Example using any Encoder Input with Pulse-drop CounterWhen enabled, the triggered camera acquires one scan line for each shaft encoder pulse-edge. Tooptimize the web application, a second Sapera parameter defines the number of triggers to skipbetween valid acquisition triggers. The figure below depicts a system where a valid camera triggeris any pulse edge from either shaft encoder signal. After a trigger, the two following triggers areignored (as defined by the Sapera pulse drop parameter).K D D K D D K D D K D D K D DShaft Encoder phase AShaft Encoder phase BK = KeepD = Drop or SkipNote: in this example, Number of trigger to drop = 2Line acquiredFigure 17: Encoder Input with Pulse-drop CounterExample using Sequential Encoder InputSupport of a dual phase encoder should consider the direction of motion of one phase signal to theother. Such a case might exist where system vibrations and/or conveyor backlash can cause theencoder to briefly travel backwards. The acquisition device must in those cases count the reversesteps and subtract the forward steps such that only pulses after the reverse count reaches zero areconsidered. By using the event “Shaft Encoder Reverse Counter Overflow”, an application canmonitor an overflow of this counter.The example figure below shows shaft encoder signals with high jitter. If the acquisition istriggered when phase B follows phase A, with jitter present phase B may precede phase A. Use ofthe Shaft Encoder Direction parameter will prevent false trigger conditions.Shaft Encoder phase AShaft Encoder phase BFigure 18: Using Shaft Encoder Direction ParameterNote: Modify camera file parameters easily with the Sapera CamExpert program.
